TThread.resume is deprecated in Delphi-2010 what should be used in place?

Question

In my multithread application

I use TThread.suspend and TThread.resume

Since moving my application to Delphi 2010 I get the following warring message

[DCC Warning] xxx.pas(277): W1000 Symbol ‘Resume’ is deprecated

If Resume is deprecated what should be used in place?

EDIT 1:

I use the Resume command to start the thread - as it is Created with 'CreateSuspended' set to True and Suspend before I terminate the thread.

EDIT 2:

Here is a link the delphi 2010 manual

Answer 1

Use TThread.Start instead of .Resume

--EDIT-- Start can of course only be used with Delphi 2010 (and later, presumably) to start a thread that was created suspended (where you would have used Resume before).

Using Resume/Suspend (or corresponding WinAPI functions) for thread synchronisation is NOT recommended. See the discussion here (have a look at Barry Kelly's comments).

Answer 2

Charles if do you read the code of TThread class , do you find the answer.

   TThread = class  
   private type  

..
..
..   
   public  
     constructor Create(CreateSuspended: Boolean);  
     destructor Destroy; override;  
     procedure AfterConstruction; override;  
     // This function is not intended to be used for thread synchronization.  
     procedure Resume; deprecated;  
     // Use Start after creating a suspended thread.  
     procedure Start;  
     // This function is not intended to be used for thread synchronization.  
     procedure Suspend; deprecated;  
     procedure Terminate;

See this link http://wings-of-wind.com/2009/08/28/rad-studio-2010-community-pulse-the-day-after-part-2/

Edit:

If you need to synchronize threads, you can use a scheme based on TMutex, TEvent and critical sections.

Bye.

Answer 3

Thread behavior control code should lie with in a thread procedure. Use appropriate sync objects and corresponding API calls in order to suspend/resume thread execution. Doing it from outside is a dangerous practice. So there was a decision to depricate it.

Answer 4

Suspend and Resume were (or used to be) potentially broken in the TThread class (if you look at the source you will see that the Suspend method directly and unconditionally sets a Boolean to indicated thread suspended state rather than more robustly deriving this state from the execution count on the thread handle. Ironically the Resume method does use this more robust indicator to update the suspended state Boolean).

This is possibly why they have been deprecated. It's also why I implemented my own class to encapsulate a Windows thread with a more robust suspend and resume mechanism as well as the ability to Restart a thread once it had completed.

I'm not sure why their deprecation is supposedly related to synchronization. Suspending and resuming threads is not necessarily related to synchronization, although I can see how it might be. It's interesting to note that the equivalent methods in the .NET framework Thread class are similarly marked as obsoleted. And the same comments w.r.t synchronization appear in the Windows API documentation for thread suspend/resume.

If using deprecated methods makes you nervous and you still wish to suspend/resume you could always use the Windows API to suspend and resume the thread by reference to it's handle.

Answer 5

See http://stackoverflow.com/questions/2097316/with-what-delphi-code-should-i-replace-my-calls-to-deprecated-tthread-method-susp

Answer 6

You should create the thread as follows:

constructor TSignalThread.Create;
begin
 // create event handle first!
  FEventHandle := CreateEvent(
          {security}      nil,
          {bManualReset}  true,
          {bInitialState} false,
          {name}          nil);
  FWaitTime := 10;
  inherited Create({CreateSuspended}false);
end;

This way a call to Start is not required.

See http://www.gerixsoft.com/blog/delphi/creating-threads for an explanation why this code works.